title: Copeptin in the differential diagnosis of the polydipsia-polyuria syndrome--revisiting the direct and indirect water deprivation tests.
abstract: BACKGROUND
  The water deprivation test (WDT) with direct or indirect measurement of plasma arginine vasopressin (AVP) is the method of choice for the differential diagnosis of the polydipsia-polyuria syndrome. In theory, direct measurement of AVP is highly attractive but is hampered by technical difficulties.
  
  
  OBJECTIVE
  The aim of the study was to evaluate the utility of copeptin, a surrogate of AVP secretion, in the diagnostic work-up of the polyuria-polydipsia syndrome and to compare its performance with the current diagnostic standard.
  
  
  METHODS
  In two tertiary referral centers, 20 healthy subjects and 50 patients with polydipsia-polyuria syndrome underwent WDT with measurements of both plasma AVP and copeptin levels. The reference diagnosis was based on clinical information and treatment response.
  
  
  RESULTS
  Twenty-two patients (44%) were diagnosed with primary polydipsia, 17 (34%) with partial central diabetes insipidus (DI), nine (18%) with complete central DI, and two (4%) with nephrogenic DI. The indirect WDT led to a correct diagnosis in 35 of 50 patients (70%). The direct WDT with AVP or copeptin measurement correctly diagnosed 23 patients (46%) or 36 patients (72%), respectively. Baseline copeptin values greater than 20 pmol/liter identified patients with nephrogenic DI, and concentrations below 2.6 pmol/liter indicated complete central DI. The ratio between Δ copeptin (0800 to 1600 h) and serum sodium concentration at 1600 h yielded optimal diagnostic accuracy, allowing us to also discern partial central DI from primary polydipsia (sensitivity 86%, and specificity 100%).
  
  
  CONCLUSIONS
  Copeptin holds promise as a diagnostic tool in the polyuria-polydipsia syndrome, improving significantly the diagnostic accuracy of the direct WDT.
authors.affiliation: Department of Internal Medicine I–Endocrine Unit, University Hospital Würzburg, Oberdürrbacher Strasse 6, D-97080 Würzburg, Germany.
authors.forename: Wiebke
authors.initials: W
authors.lastname: Fenske
authors.forename: Marcus
authors.initials: M
authors.lastname: Quinkler
authors.forename: Daniela
authors.initials: D
authors.lastname: Lorenz
authors.forename: Kathrin
authors.initials: K
authors.lastname: Zopf
authors.forename: Ulrike
authors.initials: U
authors.lastname: Haagen
authors.forename: Jana
authors.initials: J
authors.lastname: Papassotiriou
authors.forename: Andreas F H
authors.initials: AF
authors.lastname: Pfeiffer
authors.forename: Martin
authors.initials: M
authors.lastname: Fassnacht
authors.forename: Stefan
authors.initials: S
authors.lastname: Störk
authors.forename: Bruno
authors.initials: B
authors.lastname: Allolio
mesh_terms: D000328:Adult; D001127:Arginine Vasopressin / Q000097:blood; D003919:Diabetes Insipidus / Q000175:diagnosis; D003937:Diagnosis, Differential; D005260:Female; D006020:Glycopeptides / Q000097:blood*; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D011141:Polyuria / Q000175:diagnosis*; D011863:Radioimmunoassay; D012016:Reference Values; D015203:Reproducibility of Results; D013577:Syndrome; D014868:Water Deprivation / Q000502:physiology*
chemical_list: D006020:Glycopeptides; C048197:copeptins; D001127:Arginine Vasopressin